A Brief History of Pretty Pictures
Prior to the invention of the telescope the observable universe was just a myriad of pinpricks of light, those that were stationary and unchanging were called the stars, those that wandered through the sky were named the planets. People believed that the Earth was the centre of the universe and that wandering celestial bodies orbited around us whilst the stars formed a fixed shell at the outer edge of the universe. Galileo changed this view, by pointing his new telescope at the planets. No longer were the planets pin-pricks of light but were seen to be circular bodies, or in the case of Venus and Mercury shaped like the crescent-moon. Furthermore through his telescope Galileo discovered that Jupiter was circled by four points of light - which we now name the Galilean moons of Jupiter. This informed him that smaller bodies orbited around larger bodies, and hence the heliocentric model for the universe was developed. Though at this time the stars were still formed the limit and our entire knowledge of the universe outside our solar system.
It was the development of the reflector telescope that showed us the universe was more than just stars and planets. As Will mentioned in the first week’s talk the problem with refractor telescopes such as Galileo’s is that because they absorb light they can only be used successfully to examine bright celestial objects such as the planets. Reflector telescopes can collect a lot of light so they not only magnify objects, but also make them appear brighter.
A French astronomer Charles Messier in 1758 used his large reflecting telescope to meticulously scan the sky, cataloguing any objects that did not appear to be just single pin-pricks of light. In total he found over a hundred objects, which consisted of clusters of stars, some fairly loose, others very densely packed, and faint fuzzy patches which he called nebulosities, now some of these nebulosities were surrounding star clusters and others seemed not to contain any stars. Of the later type of nebulae, some appeared very circular, just as a planet appears through a telescope, though much dimmer, and hence were named planetary nebulae. Other nebulae appear to contain faint spiral structure, and others were just amorphous blobs.
Now turn your attention to the object on the lower-most object on the left side. This is the Eagle Nebula – M16.